The Feeding Ecology of Five Flatfish Species (Pleuronectiformes) in Wellington Harbour, New Zealand

Abstract

The feeding ecology of adult Rhombosolea plebeia, R.leporine, Peltorhamphus novaezeelandiae, Pelotretis flavilatus (Rhombosoleinae) and Arnoglossus scapha (Bothidae) in Wellington harbour is investigated. Extensive gut content samples collected monthly are analysed to compare the diets and feeding habits of each species. The feeding apparatus, sensory systems, brain morphology and feeding behaviour of each species are examined to ascertain their relationship to the dietary findings. The results show that the diet of the each species has a different emphasis in terms of the food items consumed, and it is possible to recognize two broad patterns of food items consumed, and it is possible to recognize two broad patterns of food resource division within this group of species. Firstly, Rhombosoleinae feed on benthic infauna and epifauna while Bothidae feed on benthic epifauna and pelagic prey. This pattern reflects differences in morphological specialization to the benthic mode of life, between bottom feeding flatfish and pelagic feeding flatfish. Secondly, R.plebeia, R.leporina and P.novaezeelandiae have relatively generalized diets largely comprising “inactive” prey while pe.flavilatus and A.scapha have relatively specialized diets, largely comprising “active” prey. This pattern reflects differences in feeding apparatus, but more importantly, differences in sensory systems indicative of different feeding methods. R.plebeia, R.leporine and P.novaezeelandiae have extensive external taste buds which facilitate non-visual prey location. These are lacking in Pe.flavilatus and A.scapha, but these two species have relatively large prominent eyes which facilitate visual prey location. It is apparent from their diets that R.plebeia, R.leporine and P.novaezeelandiae mostly select food non-visually, while Pe.flavilatus and A.scapha mostly select food visually. The lateral line system is well developed in all five species, but R.plebeia, R.leporina and particularly P.novaezeelandiae mostly select food visually. The lateral line system is well developed in all five species, but R.plebeian, R.leporina and particularly P.novaezeelandiae also have superficial neuromasts which are probably used during prey location. Relatively enlarged portions of the brain in each species correspond to specific sensory systems involved in feeding. These same species in other areas of New Zealand show different patterns of resource division and it is concluded that high turbidity is a major influencing factor in the realization of food requirements by flatfish in Wellington harbour. Because of separation in terms of food and flatfish distribution there is little evidence for competitive feeding between the study species in this locality.